1. Field of the Invention
The present invention relates to a ball grid array (BGA) packaging method for an integrated circuit (IC), more particularly, to an improved BGA packaging method, by which a packaged IC having excellent heat dissipation, a small thickness, and high reliability is provided with a simple process.
2. Description of Related Art
FIGS. 2A to 2H show respective steps of a conventional BGA packaging method. Firstly, as shown in FIG. 2A, a double-side printed circuit board (PCB), which is a substrate plate 70 having both sides thereof respectively laminated with copper foils 71, is cut and drilled to defined through-holes 711. Then in FIG. 2B, inner walls of the through-holes are plated with copper 712.
Then, as shown in FIG. 2C, dry films 721 are respectively provided to the two opposite sides of the circuit board to form patterns of circuits on the two opposite sides.
Subsequentially, referring to FIG. 2D, proper positions of the circuit board are provided with solder resist 72, the holes at the proper positions are also filled with the solder resist 72. The exposed portions, which are not covered by the solder resist 72 are plated with gold.
As shown in FIG. 2E, the through-holes 711 in the central position of the circuit board are filled with conductive paste 73, and a chip 74 is attached thereto. The conductive paste 73 filled into the through-holes 711 conducts the copper foils 71 on the two opposite sides for the purpose of heat dissipation.
The next step is wire bonding. Referring to FIG. 2F, fine gold wires 75 are connected between the chip 74 and the circuit on the PCB.
Then the chip 74 and the wires 75 are encapsulated by plastic 76, as shown in FIG. 2G. Such operation needs a mold and the plastic is injected into the mold to form a shield for protecting the chip 74 and wires 75.
Finally, solder balls 77 are attached to proper positions of the circuit board, as shown in FIG. 2H.
However, the conventional BGA packaging method has some drawbacks:
1. Such method utilizes the double-side circuit board, so the step of drilling through-holes is necessary, and the operation of filling the through-holes with solder resist or conductive paste may be unreliable. PA1 2. The heat generated by the chip must be dissipated via the conductive paste, thus the effect of heat dissipation is insufficient. If a defect occurs in the conductive paste filled into the through-holes, the heat dissipation will be even more degraded. PA1 3. It is necessary to fabricate a mold for the step of providing plastic to encapsulate the chip. PA1 4. The thickness of the packaged product is considerable. PA1 5. The capability of plastic to transfer heat is poor, so gold wires bonded on board side are easily slipped off, causing a problem of poor connection.
6. It is not possible to add a ground layer to the packaged IC, therefore the electrical characteristics of the package are not satisfactory.
7. It is not possible to form dense circuits on the circuit board of the IC since there are a plurality of through-holes therein.
Accordingly, the present invention is provided to solve the above problems.